Relationship Between Cytokine Level and Viral Load in Severe Fever with Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is a viral hemorrhagic fever caused by the SFTS virus (SFTSV), a tick-borne Phlebovirus. This study investigates the association between viral load and cytokine levels in patients with SFTS.

Viral RNA was isolated from plasma collected in EDTA and quantified by real-time reverse transcription-polymerase chain reaction (RT-PCR). Cytokines in the sera of SFTS patients were measured using cytometric bead array (CBA).

Viral loads ranged from 2.3 × 10³ copies/mL to 7.9 × 10¹¹ copies/mL. Of the 46 patients, 10 (21.7%) died during treatment. Viral loads were ≥1 × 10⁸ copies/mL in the patients who died. The concentrations of G-CSF, IFN-α, IFN-γ, IL-1β, IL-6, IL-10, MCP-1, and IP-10 were higher in patients with high viral loads. The levels of IFN-α, IFN-γ, IL-6, MCP-1, and IP-10 positively correlated with SFTSV viral load.

SFTSV RNA load was significantly correlated with the concentration of IFN-α, as well as other cytokines (IFN-γ, IL-6, MIP-1α, and IP-10).